Methods for determining reactive index for cementitious components, associated compositions, and methods of use

ABSTRACT

A variety of methods and compositions are disclosed, including, in one embodiment, a settable composition comprising: water; and a cementitious component having a calculated reactive index.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/657,060 filed Mar. 13, 2015 which is a continuation of U.S.patent application Ser. No. 13/662,155, filed on Oct. 26, 2012, nowissued as U.S. Pat. No. 8,997,578 the entire disclosures of which areincorporated herein by reference.

BACKGROUND

The present invention relates to cementitious components and, moreparticularly, in certain embodiments, to methods of determining areactive index for cementitious components.

In general, well treatments include a wide variety of methods that maybe performed in oil, gas, geothermal and/or water wells, such asdrilling, completion and workover methods. The drilling, completion andworkover methods may include, but are not limited to, drilling,fracturing, acidizing, logging, cementing, gravel packing, perforatingand conformance methods. Many of these well treatments are designed toenhance and/or facilitate the recovery of desirable fluids from asubterranean well. These fluids may include hydrocarbons such as oiland/or gas.

In cementing methods, such as well construction and remedial cementing,settable compositions are commonly utilized. As used herein, the term“settable composition” refers to a composition(s) that hydraulicallysets or otherwise develops compressive strength. Settable compositionsmay be used in primary cementing operations whereby pipe strings, suchas casing and liners, are cemented in well bores. In performing primarycementing, a settable composition may be pumped into an annulus betweena subterranean formation and the pipe string disposed in thesubterranean formation or between the pipe string and a larger conduitdisposed in the subterranean formation. The settable composition shouldset in the annulus, thereby forming an annular sheath of hardened cement(e.g., a cement sheath) that should support and position the pipe stringin the well bore and bond the exterior surface of the pipe string to thewalls of the well bore or to the larger conduit. Settable compositionsalso may be used in remedial cementing methods, such as the placement ofcement plugs, and in squeeze cementing for sealing voids in a pipestring, cement sheath, gravel pack, formation, and the like. Settablecompositions may also be used in surface applications, for example,construction cementing.

Settable compositions for use in subterranean formations may typicallyinclude a cementitious component which hydraulically sets, or otherwisehardens, to develop compressive strength. Examples of cementitiouscomponents that can be included in settable compositions includePortland cement, calcium aluminate cement, cement kiln dust, lime kilndust, fly ash, slag, pumice, and rice-hull ash, among others. Theperformance of these different cementitious components in settablecompositions may vary and can even vary for a particular cementitiouscomponent depending, for example, on the particular type or source ofthe component. For example, certain of these cementitious components mayhave undesirable properties that can make them unsuitable for use inwell treatments. In addition, variation of the performance for thecementitious components can lead to lack of predictability andconsistency for the cementitious components when used in treatmentfluids. This lack of predictability consistency may even be apparent forthe same cementitious component, for example, if sourced from differentlocations.

SUMMARY

The present invention relates to cementitious components and, moreparticularly, in certain embodiments, to methods of determining areactive index for cementitious components.

An embodiment discloses a method of cementing comprising: providing asettable composition comprising water and a cementitious componenthaving a determined reactive index; and allowing the settablecomposition to set to form a hardened mass.

Another embodiment discloses a method of measuring reactivity of acementitious component comprising: measuring a parameter of thecementitious component, the cementitious component having a specificsurface area; and dividing the measured parameter by the specificsurface area of the cementitious component to obtain a reactive indexfor the cementitious component.

Another embodiment discloses a settable composition comprising: water;and a cementitious component having a calculated reactive index.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present invention, and should not be used to limit or define theinvention.

FIG. 1 is a chart showing measured reactive indexes for various supplysources of cement kiln dust.

FIG. 2 is a chart comparing actual versus predicted compressive strengthfor dry blends of cement kiln dust.

FIG. 3 is a chart comparing actual versus predicted volume averageapparent viscosity at 511 sec⁻¹ for dry blends of cement kiln dust.

FIG. 4 is a chart comparing actual versus predicted volume averageapparent viscosity at 51 sec⁻¹ for dry blends of cement kiln dust.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to cementitious components and, moreparticularly, in certain embodiments, to methods of determining areactive index for cementitious components. By determining the reactiveindex for cementitious components, blends of cementitious components maybe used in well treatments, according to particular embodiments, thatcan provide more predictable and consistent performance. In addition,additional embodiments may include using the determined reactive indexto provide blends of cementitious components in which one or moreparameters have been optimized, including compressive strength, Young'sModulus, fluid loss, and/or thickening time, for example.

Without being limited by theory, the reactive index of a cementitiouscomponent may be referred to as a measure of the cementitiouscomponent's reactivity as adjusted for differences in surface area.Example techniques for determining the reactive index may comprisemeasuring a parameter of the cementitious component, and then dividingthe measured parameter by the specific surface area of the cementitiouscomponent. In some embodiments, the reactive index for a cementitiouscomponent may be calculated in accordance with the following equation:RI=MP/SSAwherein RI is the reactive index, MP is the measured parameter of thecementitious component, and SSA is the specific surface area of thecementitious component. In general, specific surface area is a propertyof a particulate solid and, as used herein, is defined as the totalsurface area of the cementitious component divided by the mass of thecementitious component or the total surface area divided by the bulkvolume of the cementitious component.

In general, cementitious components are particulate solids thathydraulically set, or otherwise harden, to develop compressive strengthin the presence of water. Non-limiting examples of cementitiouscomponents that may be suitable for use in embodiments of the presentinvention include Portland cements, calcium aluminate, gypsum,pozzolanic materials, and kiln dust. Mixtures of one or more differentcementitious components may also be used. In some embodiments, thecementitious component may be combined with lime.

In some embodiments, the cementitious component may comprise Portlandcement. Portland cement is a commonly used cementitious component thathydraulically reacts with water to develop compressive strength.Examples of suitable Portland cements may include those classified asClasses A, C, G and H cements according to American Petroleum Institute,API Specification for Materials and Testing for Well Cements, APISpecification 10, Fifth Edition, Jul. 1, 1990. In addition, Portlandcements suitable for use in embodiments of the present invention mayalso include those classified as ASTM Type I, I/II, II, III, IV, or V.In some embodiments, blends of cementitious components containingPortland cement may be used.

In some embodiments, the cementitious component may comprise a calciumaluminate. Calcium aluminate may hydraulically react with water todevelop compressive strength. Calcium aluminate may be included incements commonly referred to as calcium aluminate cements or highalumina content cements. Calcium aluminate cements may be prepared in amanufacturing process that includes mixing a calcium bearing material(e.g., limestone) and an aluminum-bearing material (e.g., bauxite).

In some embodiments, the cementitious component may comprise gypsum.Gypsum is a material that sets in the presence of water to developcompressive strength. Gypsum may be included in cements commonlyreferred to as gypsum cements. For use in cements, gypsum may, in someinstances, be burned at extremely high temperatures and then ground. Inparticular embodiments, gypsum may be added to Portland cement.

In some embodiments, the cementitious component may comprise apozzolanic material. Pozzolanic materials that may be suitable for useinclude a wide variety of natural or artificial materials that exhibitcementitious properties in the presence of calcium hydroxide. Examplesof suitable pozzolanic material that may be suitable for use inembodiments of the present invention include natural and artificialpozzolans, such as fly ash, silica fume, slag, burned shale, burnedclay, metakaolin, pumice, diatomaceous earth, volcanic ash, opalineshale, tuff, and burned organic materials, such as agricultural wasteash, municipal waste ash (e.g., municipal solid waste ash), waste-watertreatment waste ash, animal waste ash, non-human-non-animal industrialwaste ash, and combinations thereof. Specific examples of agriculturalwaste ash include, for example, rice husk ash, wood (e.g., sawdust,bark, twigs, branches, other waste wood) ash, tree leave ash, corn cobash, cane (e.g., sugar cane) ash, bagasse ash, grain (e.g., amaranth,barley, corn flaxseed, millet, oat, quinoa, rye, wheat etc.) and relatedby-product(s) (e.g., husks, hulls, etc.) ash, orchard ash, vine trimmingash, grass (e.g., Korai, Tifton, native shiba, etc.) ash, straw ash,ground nut shell ash, legume (e.g., soybean) ash, and combinationsthereof.

In some embodiments, the cementitious component may comprise a kilndust. One example of a kiln dust includes cement kiln dust. Cement kilndust, as that term is used herein, refers to a partially calcined kilnfeed which is removed from the gas stream and collected, for example, ina dust collector during the manufacture of cement. The cement kiln dustgenerally may exhibit cementitious properties, in that it may set andharden in the presence of water. Usually, large quantities of cementkiln dust are collected in the production of cement that are commonlydisposed of as waste. Disposal of the cement kiln dust can addundesirable costs to the manufacture of the cement, as well as theenvironmental concerns associated with its disposal. The chemicalanalysis of the cement kiln dust from various cement manufactures variesdepending on a number of factors, including the particular kiln feed,the efficiencies of the cement production operation, and the associateddust collection systems. Cement kin dust generally may comprise avariety of oxides, such as SiO2, Al₂O₃, Fe₂O₃, CaO, MgO, SO₃, Na₂O, andK₂O. Another example of a kiln dust includes lime kiln dust. Lime kilndust, as that term is used herein, refers to a product generated in themanufacture of lime. The lime kiln dust may be collected, for example,by dust control systems in the calcination of lime stone.

In some embodiments, one or more parameters of the cementitiouscomponent may be measured and then used in determining the reactiveindex. The parameters may include a number of different parameters thatmay be measured using standard laboratory testing techniques for asettable composition comprising a cementitious component and water.Additional components may also be included in the settable compositions,for example, to vary one or more properties of the treatment fluid.Parameters of the cementitious component, or settable compositioncontained therein, that may be measured include, for example,compressive strength, Young's Modulus, fluid loss, thickening time,rheological values (e.g., volume average apparent viscosity, plasticviscosity, yield point, etc.) and/or free water.

Compressive strength is generally the capacity of a material orstructure to withstand axially directed pushing forces. The compressivestrength of the cementitious component may be measured at a specifiedtime after the cementitious component has been mixed with water and theresultant treatment fluid is maintained under specified temperature andpressure conditions. For example, compressive strength can be measuredat a time in the range of about 24 to about 48 hours after the fluid ismixed and the fluid is maintained at a temperature of 170° F. andatmospheric pressure. Compressive strength can be measured by either adestructive method or non-destructive method. The destructive methodphysically tests the strength of treatment fluid samples at variouspoints in time by crushing the samples in a compression-testing machine.The compressive strength is calculated from the failure load divided bythe cross-sectional area resisting the load and is reported in units ofpound-force per square inch (psi). Non-destructive methods typically mayemploy an Ultrasonic Cement Analyzer (“UCA”), available from FannInstrument Company, Houston, Tex. Compressive strengths may bedetermined in accordance with API RP 10B-2, Recommended Practice forTesting Well Cements, First Edition, July 2005.

Young's modulus also referred to as the modulus of elasticity is ameasure of the relationship of an applied stress to the resultantstrain. In general, a highly deformable (plastic) material will exhibita lower modulus when the confined stress is increased. Thus, the Young'smodulus is an elastic constant that demonstrates the ability of thetested material to withstand applied loads. A number of differentlaboratory techniques may be used to measure the Young's modulus of atreatment fluid comprising a cementitious component after the treatmentfluid has been allowed to set for a period of time at specifiedtemperature and pressure conditions.

Fluid loss typically refers to loss of a fluid such as a treatment fluidinto a subterranean formation. A number of different laboratorytechniques may be used to measure fluid loss of a treatment fluid togive an indication of the behavior of the treatment fluid in a well.Fluid loss may be measured using a static fluid-loss test, with either astatic or stirred fluid-loss cell, in accordance with theafore-mentioned API RP Practice 10B-2.

Thickening time typically refers to the time a fluid, such as atreatment fluid, comprising the cementitious component, remains in afluid state capable of being pumped. A number of different laboratorytechniques may be used to measure thickening time to give an indicationof the amount of time a treatment fluid will remain pumpable in a well.An example technique for determining whether a treatment fluid is in apumpable fluid state may use a high-temperature high-pressureconsistometer at specified pressure and temperature conditions, inaccordance with the procedure for determining cement thickening timesset forth in the afore-mentioned API RP Practice 10B-2. The thickeningtime may be the time for the treatment fluid to reach 70 Bearden unitsof consistency (“Bc”) and may be reported in time to reach 70 Bc.

Rheological values of a fluid may be determined to characterize thefluid's rheological behavior. Rheological values that may be determinedinclude volume average apparent viscosity, yield point and plasticviscosity, among others. Plastic viscosity is typically a measure of theresistance of a fluid to flow. In some embodiments, the yield point maybe a parameter of the Bingham plastic model, the yield point being theslope of the shear stress/shear rate line above the yield point. Yieldpoint is typically a measure of the point at which a material can nolonger deform elastically. In some embodiments, the yield point may be aparameter of the Bingham plastic model, the yield point being the yieldstress extrapolated to a shear rate of zero. A number of differentlaboratory techniques may be used to measure rheological values of atreatment fluid to give an indication of the behavior of the treatmentfluid in a well. Rheological values may be determined in accordance withthe procedure set forth in API RP Practice 10B-2.

Free water typically refers to any water in a fluid that is in excess towhat is required to fully hydrate the components of the fluid. Freewater can be undesired as it may physically separate from a cementcomposition as it sets. Free water may also be referred to as freefluid. A number of different laboratory techniques may be used tomeasure free water of a treatment fluid to give an indication of thebehavior of the treatment fluid in a well. Free water may be determinedin accordance with the procedure set forth in API RP Practice 10B-2.

As previously mentioned, the reactivity of cementitious components mayvary between different types of cementitious components or even betweendifferent sources for a particular type of cementitious component. Forexample, the reactivity of Portland cement and another cementitiouscomponent, such as a pozzolanic material, may be different. By way offurther example, the reactivity of a cementitious component may varybetween different sources for the cementitious component. In someembodiments, the reactive index of the cementitious component may varybetween two or more different sources by a factor of at least about 2:1.For example, the reactive index of the cementitious component betweendifferent sources may vary by an amount between any of and/or includingany of about 2:1, about 10:1, about 50:1, about 100:1, about 250:1,about 500:1, or about 1000:1. Because the reactivity varies betweendifferent cementitious components and even between different sources fora cementitious component, the performance of different cementitiouscomponents may be unpredictable and may also lead to a lack ofconsistency for the cementitious components when used in treatmentfluids such as settable compositions. In some instances, the performanceof a particular cementitious component may have undesirable properties,which may make it unsuitable for use. For example, a cementitiouscomponent from a particular source may have properties making itundesirable for use.

In some embodiments, a blend of two or more different cementitiouscomponents may be used to provide a blended cementitious component thatmay have properties suitable for use in a particular application. Thismay be particularly useful, for example, where one of the cementitiouscomponents in the blend may have properties making it unsuitable forparticular applications. For example, a cementitious component such ascement kiln dust from a first source may be blended with a cementitiouscomponent such as cement kiln dust from a second source. In someembodiments, one or both of the cementitious components may havereactivities that are unsuitable for a particular application. Forexample, the reactivities of each cementitious component may beindividually too slow or too fast for a particular application. Theblends of the cementitious component from the two different sources mayform a blended cementitious component having compressive strengthproperties that are suitable for the application. In some embodiments,the relative proportions (e.g., weight fractions) of each cementitiouscomponent in the blended cementitious component may then be adjusted toadjust the compressive strength properties of the blended cementitiouscomponent.

The two or more cementitious components in the blended cementitiouscomponent may include, for example, two or more different types ofcementitious components, such as Portland cement and cement kiln dust.Alternatively, the two or more cementitious components in the blendedcementitious component may include, for example, a cementitiouscomponent from two or more different sources. For example, a firstcementitious component may comprise cement kiln dust from a firstsource, and the second cementitious component may comprise cement kilndust from a second source. It should be understood that embodiments arenot limited to only two different sources, but may include acementitious component, such as cement kiln dust, from three, four,five, or even more different sources. The two or more different sourcesfor the cementitious component may include different manufactures,different cement manufacturing plants, and the like. A cementitiouscomponent, such as cement kiln dust which is a byproduct from the cementmanufacturing plant, may have a number of different sources availablethroughout the world. For example, different sources for cement kilndust may include different manufacturing plants throughout the world atwhich cement kiln dust can be generated.

The two or more cementitious components may be blended to form theblended cementitious component, for example, prior to combination withwater and/or other components of the treatment fluid. In particularembodiments, the two or more cementitious components may be dry blendedto form a dry blend comprising the two or more cementitious components.The dry blend may then be combined with water and/or other components,in any order, to form the treatment fluid. However, the use of the term“blend” is not intended to imply that the two or more cementitiouscomponents have been dry blended prior to combination with water. Forexample, the blend of two or more cementitious components may not becombined until after one, or even both, of the cementitious componentshas already been blended with water.

In some embodiments, the reactive index may be used to optimize theblended cementitious component, wherein the blended cementitiouscomponent comprises two or more cementitious components. For example,the reactive index may be used to optimize one or more parameters of theblended cementitious component, including compressive strength, Young'sModulus, fluid loss, and/or thickening time. Optimizing the blendedcementitious component may include determining the reactive index foreach of the cementitious components in the blended cementitiouscomponent. The reactive indexes for the cementitious components may thenbe used to predict the performance of the blended cementitiouscomponent. The ratio of each cementitious component may be adjusted tooptimize the performance of the blended cementitious component. Theperformance of the blended cementitious component may be optimized withthe performance of the blended cementitious component estimated usingthe following equation:

${EP}_{blend} = {\sum\limits_{i = 1}^{n}{\left( {RI}_{i} \right)\left( {SSA}_{i} \right)\left( f_{i} \right)^{m}}}$Wherein EP_(blend) is the estimated parameter for the blendedcementitious component, i is the individual cementitious component fromthe set of cementitious components 1 to n, n is an integer, RI_(i) isthe reactive index for cementitious component i, SSA_(i) is the specificsurface area for cementitious component i, f_(i) is the mass fraction ofthe cementitious component i, and wherein m is a number from 1 to 10.The set of cementitious components may include 2 or more differentcementitious components. The two or more different cementitiouscomponent may be different types of cementitious components, such asPortland cement and slag, or may be from different sources, such ascement kiln dust from a first source and cement kiln dust from a secondsource. In some embodiments, m may be 1. In alternative embodiments, mmay be 7/3.

In some embodiments, the mean particle size of the cementitiouscomponent may be altered from its original particle size. The reactiveindex may then be measured for the altered cementitious component. Thealtered cementitious component may be included in a blended cementitiouscomponent. In accordance with present embodiments, the mean particlesize of the cementitious component can be altered using any suitabletechnique, including, without limitation, grinding or separating toprovide a material having an altered particle size. Separating thecementitious component may include sieving or any other suitabletechnique for separating the cementitious component to provide a meanparticle size that has been altered from its original size. For example,sieving may be used to produce cementitious component having anincreased or reduced mean particle size as desired for a particularapplication. By way of further example, grinding may be used to decreasethe mean particle size of the cementitious component. Combinations ofgrinding and separating may be used in some embodiments. The term“ground” or “grinding” as used herein means using a grinder (e.g., ballmill, rod mill, etc.) to reduce the particle size of the specifiedcomponent(s). An example of a suitable grinder is an 8000 Mixer/Mill®ball mill, available from SPEX Sample Prep. In some embodiments, thecementitious component may be ground for a time period in a range offrom about 30 minutes to about 1 hour.

The mean particle size of the cementitious component can be altered toany size suitable for use in cementing operations. In some embodiments,the mean particle size of the cementitious component may be altered fromits original particle size to have a mean particle size in a range ofabout 1 micron to about 350 microns. The mean particle size correspondsto d50 values as measured by particle size analyzers such as thosemanufactured by Malvern Instruments, Worcestershire, United Kingdom.

In some embodiments, the mean particle size of the cementitiouscomponent may be increased from its original size. For example, the meanparticle size of the cementitious component may be at least 5% greaterthan its original size. In some embodiments, at least a portion of thecementitious component may be increased to a size that is in a range offrom about 5% to about 500% greater than its original size. In someembodiments, the mean particle size may be increased to a size rangingbetween any of and/or including any of about 5%, about 10%, about 20%,about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about90%, about 100%, about 200%, about 300%, about 400%, or about 500%greater than its original size.

In some embodiments, the mean particle size of the cementitiouscomponent may be reduced from its original size. For example, the meanparticle size may be reduced in an amount sufficient to increase thecompressive strength of the cementitious component. In some embodiments,the cementitious component may have a mean particle size that is atleast 5% less than its original size. In some embodiments, at least aportion of the cementitious component may be reduced to have a meanparticle size in a range of from about 5% to about 95% of its originalsize. For example, the mean particle size may be reduced to a sizeranging between any of and/or including any of about 5%, about 10%,about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about45%, about 50%, about 55%, about 60%, about 6%, about 70%, about 75%,about 80%, about 90%, or about 95% of its original size. By way ofexample, the reduced particle size cementitious component may have amean particle size of less than about 15 microns. In some embodiments,the reduced particle size cementitious component may have a meanparticle size of less than about 10 microns, less than about 5 microns,less than about 4 microns, less than about 3 microns, less than about 2microns, or less than about 1 micron. In specific embodiments, thereduced particle size cementitious component may have a mean particlesize in a range of from about 0.1 microns to about 15 microns, fromabout 0.1 microns to about 10 microns, or from about 1 micron to about10 microns. One of ordinary skill in the art, with the benefit of thisdisclosure, should be able to select a particle size for thecementitious component suitable for a particular application.

In some embodiments, the mean particle size of the cement kiln dust maybe reduced in an amount sufficient to provide an increase in compressivestrength for the settable composition. For example, the mean particlesize may be reduced to provide an increase in compressive strength of atleast about 5%, about 25%, about 50%, about 75%, or about 100%.

In accordance with present embodiments, the cementitious components maybe included in treatment fluids that can be used in a variety ofoperations that may be performed in subterranean formations. Thecementitious component may have reactive index calculated according todisclosed embodiments. In some embodiments, a blended cementitiouscomponent may be used. In some embodiments, the reactive index may beused in determining the cementitious components in a particular blendedcementitious component. As referred to herein, the term “treatmentfluid” will be understood to mean any fluid that may be used in asubterranean application in conjunction with a desired function and/orfor a desired purpose. The term “treatment fluid” is not intended toimply any particular action by the fluid. Treatment fluids often areused in, e.g., well drilling, completion, and stimulation operations.Examples of such treatment fluids include drilling fluids, well cleanupfluids, workover fluids, conformance fluids, gravel pack fluids,acidizing fluids, fracturing fluids, cement compositions, spacer fluids,and the like.

While embodiments of the compositions and methods may be used in avariety of applications, they may be particularly useful forsubterranean well completion and remedial operations, such as primarycementing of casings and liners in well bores. They also may be usefulfor surface cementing operations, including construction cementingoperations. Accordingly, embodiments of the present invention disclosesettable compositions comprising a cementitious component and water.

The cementitious component may be included in embodiments of thesettable compositions in an amount suitable for a particularapplication. In some embodiments, the cementitious component maycomprise cement kiln dust. The cement kiln dust may be present in anamount in a range of from about 0.01% to 100% by weight of thecementitious component (“bwoc”). For example, the cement kiln dust maybe present in an amount ranging between any of and/or including any ofabout 0.01%, about 5%, about 10%, about 20%, about 30%, 40%, about 50%,about 60%, about 70%, about 80%, about 90%, or about 100%. Thecementitious component may be free or essentially free (for example, nomore than 1% by weight of the cementitious component) of any additionalcementitious components other than the cementitious component. In someembodiments, the cementitious component may be essentially free ofPortland cement. One of ordinary skill in the art with the benefit ofthis disclosure should be able to determine an appropriate amount of thecementitious component to include for a particular application.

The water used in embodiments of the settable compositions of thepresent invention may include, for example, freshwater, saltwater (e.g.,water containing one or more salts dissolved therein), brine (e.g.,saturated saltwater produced from subterranean formations), seawater, orany combination thereof. Generally, the water may be from any source,provided, for example, that it does not contain an excess of compoundsthat may undesirably affect other components in the settablecomposition. In some embodiments, the water may be included in an amountsufficient to form a pumpable slurry. In some embodiments, the water maybe included in the settable compositions of the present invention in anamount in a range of from about 40% to about 200% bwoc. For example, thewater may be present in an amount ranging between any of and/orincluding any of about 50%, about 75%, about 100%, about 125%, about150%, or about 175% by weight of the cement. In specific embodiments,the water may be included in an amount in the range of from about 40% toabout 150% bwoc. One of ordinary skill in the art, with the benefit ofthis disclosure, will recognize the appropriate amount of water toinclude for a chosen application.

Other additives suitable for use in subterranean cementing operationsmay also be added to embodiments of the settable compositions, inaccordance with embodiments of the present invention. Examples of suchadditives include, but are not limited to, fluid-loss-control additive,set retarder, strength-retrogression additives, set accelerators,weighting agents, lightweight additives, gas-generating additives,mechanical-property-enhancing additives, lost-circulation materials,filtration-control additives, foaming additives, thixotropic additives,and any combination thereof. Specific examples of these, and other,additives include crystalline silica, amorphous silica, fumed silica,salts, fibers, hydratable clays, calcined shale, vitrified shale,microspheres, hollow glass spheres, fly ash, diatomaceous earth,metakaolin, ground perlite, rice husk ash, natural pozzolan, zeolite,cement kiln dust, resins, any combination thereof, and the like. Aperson having ordinary skill in the art, with the benefit of thisdisclosure, will readily be able to determine the type and amount ofadditive useful for a particular application and desired result.

Those of ordinary skill in the art will appreciate that embodiments ofthe settable compositions generally should have a density suitable for aparticular application. By way of example, embodiments of the settablecompositions may have a density of about 4 pounds per gallon (“lb/gal”)to about 20 lb/gal. In certain embodiments, the settable compositionsmay have a density of about 8 lb/gal to about 17 lb/gal. Embodiments ofthe settable compositions may be foamed or unfoamed or may compriseother means to reduce their densities, such as hollow microspheres,low-density elastic beads, or other density-reducing additives known inthe art. In addition, the settable composition may comprise weightingagents or other means to increase their densities. Those of ordinaryskill in the art, with the benefit of this disclosure, will recognizethe appropriate density for a particular application.

In some embodiments, the settable compositions may have a thickeningtime of greater than about 1 hour, alternatively, greater than about 2hours, alternatively greater than about 5 hours at 3,000 psi andtemperatures in a range of from about 50° F. to about 400° F.,alternatively, in a range of from about 80° F. to about 250° F., andalternatively at a temperature of about 140° F. In some embodiments, thesettable composition may have a 24-hour compressive strength in a rangeof from about 100 psi to about 10,000 psi and, alternatively, from about350 psi about 3,000 psi at atmospheric pressure and temperatures in arange of from about 50° F. to about 400° F., alternatively, in a rangeof from about 80° F. to about 250° F., and alternatively at atemperature of about 180° F.

The components of the settable composition may be combined in any orderdesired to form a settable composition that can be placed into asubterranean formation. In addition, the components of the settablecompositions may be combined using any mixing device compatible with thecomposition, including a bulk mixer, for example. In some embodiments, adry blend may first be formed by the cementitious component or mixtureof cementitious components. The dry blend may then be combined withwater to form the settable composition. Other suitable techniques may beused for preparation of the settable compositions as will be appreciatedby those of ordinary skill in the art in accordance with embodiments ofthe present invention.

As will be appreciated by those of ordinary skill in the art,embodiments of the cement compositions of the present invention may beused in a variety of cementing operations, including surface andsubterranean operations, such as primary and remedial cementing. In someembodiments, a cement composition may be provided that comprises acementitious component and water, and allowed set. In certainembodiments, the cement composition may be introduced into asubterranean formation and allowed to set therein. As used herein,introducing the cement composition into a subterranean formationincludes introduction into any portion of the subterranean formation,including, without limitation, into a well bore drilled into thesubterranean formation, into a near well bore region surrounding thewell bore, or into both.

In primary-cementing embodiments, for example, embodiments may compriseproviding a cement composition, introducing the cement composition intoa well-bore annulus; and allowing the cement composition to set in theannulus to form a hardened mass. The well-bore annulus may include, forexample, an annular space between a conduit (e.g., pipe string, liner,etc.) and a wall of a well bore or between the conduit and a largerconduit in the well bore. Generally, in most instances, the hardenedmass should fix the conduit in the well bore.

In remedial-cementing embodiments, a cement composition may be used, forexample, in squeeze-cementing operations or in the placement of cementplugs. By way of example, the cement composition may be placed in a wellbore to plug an opening, such as a void or crack in the formation, in agravel pack, in the conduit, in the cement sheath, and/or a microannulusbetween the cement sheath and the conduit or formation. An example ofsuch a method may comprise placing the cement composition into the void,and allowing the cement composition to set in the void.

While the preceding description is directed to the use of thecementitious component in cementing methods, it should be understoodthat embodiments of the present technique also encompasses the use ofthe cementitious component in any of a variety of different subterraneantreatments. The cementitious component may have a reactive indexdetermined according to disclosed embodiments. In some embodiments, ablended cementitious component may be used. In some embodiments, thereactive index may be used in determining the amount of cementitiouscomponents that are in a particular blended cementitious component. Anexample method may include a subterranean treatment method thatcomprises providing a treatment fluid comprising the cementitiouscomponent and introducing the treatment fluid into a subterraneanformation. For example, a drilling fluid may comprise the cementitiouscomponent, wherein the drilling fluid may be circulated downwardlythrough a drill pipe and drill bit and then upwardly through the wellbore to the surface. The drilling fluid used may be any number of fluids(gaseous or liquid) and mixtures of fluids and solids (such as solidsuspensions, mixtures, and emulsions).

In some embodiments, a spacer fluid may comprise the cementitiouscomponent, which may have a determined reactive index according todisclosed embodiments. Spacer fluids may be used, for example, in thedisplacement of fluids from well bore. In an embodiment, the fluiddisplaced by the spacer fluid comprises a drilling fluid. By way ofexample, the spacer fluid may be used to displace the drilling fluidfrom the well bore. The drilling fluid may include, for example, anynumber of fluids, such as solid suspensions, mixtures, and emulsions.Additional steps in embodiments of the method may comprise introducing apipe string into the well bore, introducing a cement composition intothe well bore with the spacer fluid separating the cement compositionand the first fluid. In an embodiment, the cement composition may beallowed to set in the well bore. The cement composition may include, forexample, cement and water. In some embodiments, at least a portion ofthe spacer fluid may be left in the well bore, the spacer fluid in thewell bore setting to form a hardened mass.

EXAMPLES

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the invention.

Example 1

The reactive indexes for compressive strength for thirty-three differentsamples of cement kiln dust, designated Samples A through GG, weredetermined and are provided in FIG. 1. The CKD samples are each from adifferent supply source. The reactive indexes for thirty-three CKDsamples were determined by dividing the determined 24-hour compressivestrength for a settable composition by the specific surface area of theCKD sample. The specific surface area for each CKD sample was determinedby dividing the total surface area of the particular CKD sample by thesample mass. The surface area was determined using a Malvern particlesize analyzer. The 24-hour compressive strength for each CKD sample wasdetermined by first preparing a settable composition that comprised theCKD sample in an amount of 100% bwoc and water in an amount sufficientto provide a density of about 13 lb/gal. After preparation, the settablecomposition was allowed to cure for 24 hours in a 2″×4″ metal cylinderthat was placed in a water bath at 170° F. to form set cement cylinders.Immediately after removal from the water bath, destructive compressivestrengths were determined using a mechanical press in accordance withAPI RP 10B-2.

Example 2

Blended cementitious components were prepared that comprised mixtures ofthe CKD samples from Example 1, as indicated in the table below. Thedetermined reactive indexes for the CKD samples were then used in thefollowing equation to predict the performance of each blendedcementitious component.CS_(blend)=(RI_(Z))(SSA_(Z))(f _(Z))^(m)+(RI_(F))(SSA_(F))(f_(F))^(m)+(RI_(E))(SSA_(E))(f _(E))^(m)Wherein CS_(blend) is the estimated compressive strength for the blendedcementitious component, RI_(Z) is the reactive index for compressivestrength for CKD Sample Z and was 6.9, m is 1, SSA_(Z) is the specificsurface area for CKD Sample Z and was 2.32, f_(Z) is the mass fractionof CKD Sample Z, RI_(F) is the reactive index for compressive strengthfor CKD Sample F and was 105, SSA_(F) is the specific surface area forCKD Sample F and was 2.33, f_(F) is the mass fraction of CKD Sample F,RI_(E) is the reactive index for compressive strength for CKD Sample Eand was 107, SSA_(E) is the specific surface area for CKD Sample E andwas 3.6, and f_(E) is the mass fraction of CKD Sample E.

The estimated compressive strength values for the blended cementitiouscomponents were then compared with the actual 24-hour compressivestrength values for the blended cementitious components. The 24-hourcompressive strength for each blended cementitious component wasdetermined by first preparing a settable composition that comprised theblended cementitious component in an amount of 100% bwoc and water in anamount sufficient to provide a density of 13 lb/gal. A cement dispersant(CFR-3™ cement friction reducer, from Halliburton Energy Services, Inc.)in an amount of from 0.5% bwoc to 1.0% bwoc was added to some of thesamples and should not impact determined compressive strength values.After preparation, the settable composition was allowed to cure for 24hours in a 2″×4″ metal cylinder that was placed in a water bath at 140°F. to form set cement cylinders. Immediately after removal from thewater bath, destructive compressive strengths were determined using amechanical press in accordance with API RP 10B-2.

A chart of the actual compressive strength values versus the estimatedcompressive strength values is provided on FIG. 2. As shown on FIG. 2,the charted values have an R² value of 0.952 and a slope of 0.9253. Theestimated and actual compressive strength values for the blendedcementitious components are also provided in Table 1 below.

TABLE 1 Estimated Actual CKD CKD CKD Compressive Compressive Sample ZSample F Sample E Strength Strength (% bwoc) (% bwoc) (% bwoc) (psi)(psi) 100 0 0 16 16 75 25 0 73 51 25 75 0 187 183 0 100 0 244 244 75 025 108 84 50 0 50 200 192 25 0 75 292 216 0 0 100 384 384

Example 3

The reactive indexes for volume average apparent viscosity at 511 sec⁻¹and 51 sec⁻¹ were determined for CKD Samples Z, F, and E from Example 1and are provided in Table 2 below. The reactive indexes for thesesamples were determined by dividing the determined volume averageapparent viscosity for a settable composition by the specific surfacearea of the CKD sample. The specific surface area for each CKD samplewas determined by dividing the total surface area of the particular CKDsample by the sample mass. The surface area was determined using aMalvern particle size analyzer. The 24-hour volume average apparentviscosity (“VAV”) for each CKD sample was determined by first preparinga settable composition that comprised the CKD sample in an amount of100% bwoc and water in an amount sufficient to provide a density ofabout 12 lb/gal. The volume average apparent viscosities were measuredat 511 1 sec⁻¹ and 51 sec⁻¹ in accordance with API RP 10B-2.

TABLE 2 CKD CKD CKD Sample Z Sample F Sample E SSA 2.32 2.33 3.6 VAV at511 sec⁻¹ (cp) 11 62 123 RI at 511 sec⁻¹ 5 27 32 VAV at 51 sec⁻¹ (cp) 40410 860 RI at 51 sec⁻¹ 17 176 239

Next, blended cementitious components were prepared that comprisedmixtures of CKD samples Z, F, E, as indicated in the table below. Thedetermined reactive indexes at 511 sec⁻¹ and 51 sec⁻¹ for the CKDsamples were then used in the following equation to predict theperformance of each blended cementitious component.VAV_(blend)=(RI_(Z))(SSA_(Z))(f _(Z))^(m)+(RI_(F))(SSA_(F))(f_(F))^(m)+(RI_(E))(SSA_(E))(f _(E))^(m)

Wherein VAV_(blend) is the estimated volume average apparent viscosityfor the blended cementitious component, RI_(Z) is the reactive index forvolume average apparent viscosity for CKD Sample Z, SSA_(Z) is thespecific surface area for CKD Sample Z, f_(Z) is the mass fraction ofCKD Sample Z, m is 7/3, RI_(F) is the reactive index for volume averageapparent viscosity for CKD Sample F, SSA_(F) is the specific surfacearea for CKD Sample F, f_(F) is the mass fraction of CKD Sample F,RI_(E) is the reactive index for volume average apparent viscosity forCKD Sample E, SSA_(E) is the specific surface area for CKD Sample E, andf_(E) is the mass fraction of CKD Sample E.

The estimated volume average apparent viscosities at 511 sec¹ and 51sec¹ for the blended cementitious components were then compared with theactual volume average apparent viscosities at 511 sec⁻¹ and 51 sec⁻¹ forthe blended cementitious components. The volume average apparentviscosities for each blended cementitious component was determined byfirst preparing a settable composition that comprised the blendedcementitious component in an amount of 100% bwoc and water in an amountsufficient to provide a density of 12 lb/gal. After preparation, thevolume average apparent viscosities at 511 sec¹ and 51 sec¹ weredetermined in accordance with API RP 10B-2.

Charts of the actual volume average viscosity values versus theestimated volume average viscosity values are provided on FIGS. 3 and 4.As shown on FIG. 3, the charted values at 511 sec¹ have an R² value of0.9894 and a slope of 0.9975. As shown on FIG. 4, the charted values at51 sec⁻¹ have an R² value of 0.9931 and a slope of 0.9814. The estimatedand actual volume average viscosity values for the blended cementitiouscomponents are also provided in Table 2 below.

TABLE 3 CKD CKD CKD Actual VAV @ Est. VAV @ Actual VAV @ Est VAV @Sample Z Sample F Sample E 511 sec⁻¹ 511 sec⁻¹ 51 sec⁻¹ 51 sec⁻¹ (%bwoc) (% bwoc) (% bwoc) (cp) (cp) (cp) (cp) 100 0 0 11.0 11.0 40.0 40.075 25 0 11.0 8.1 40.0 36.7 25 75 0 24.0 32.2 190.0 211.3 0 100 0 62.062.0 410.1 410.0 0 0 100 123.0 123.0 860.2 860.0 25 0 75 66.0 63.4 500.1441.5 50 0 50 25.0 26.7 160.0 179.0 75 0 25 16.0 10.5 60.0 54.5

It should be understood that the compositions and methods are describedin terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present invention. Ifthere is any conflict in the usages of a word or term in thisspecification and one or more patent(s) or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. A settable composition comprising: water; and ablended cementitious component, wherein the blended cementitiouscomponent comprises a first cement kiln dust from a first source havinga first reactive index, a second cement kiln dust from a second sourcehaving a second reactive index, wherein the first source and the secondsource are different, and Portland cement, wherein the first reactiveindex and the second reactive index vary by an amount between about 2:1to about 10:1 wherein, wherein the settable composition has a propertyof a 24-hour compressive strength of about 350 psi to about 3000 psi atatmospheric pressure and temperature in a range of from about 50° F. toabout 400° F., and wherein a mass fraction for the first cement kilndust and a mass fraction for the second cement kiln dust in the blendedcementitious component is based on the reactive index of the firstcement kiln dust and the reactive index of the second cement kiln dustsuch that the settable composition has the property of a 24-hourcompressive strength of about 350 psi to about 3000 psi.
 2. Thecomposition of claim 1 wherein the particle size of either the firstcementitious component, the second cementitious component, or both, hasbeen adjusted to adjust the reactive index of the cementitiouscomponent.
 3. The composition of claim 2 wherein the particle size ofeither the first cementitious component, the second cementitiouscomponent, or both, was adjusted to have a mean particle size of about 1micron to about 350 microns.
 4. The composition of claim 2 whereineither the first cementitious component, the second cementitiouscomponent, or both, comprises a ground cementitious component.
 5. Thecomposition of claim 2 wherein the particle size of either the firstcementitious component, the second cementitious component, or both, wasreduced to a mean particle of about 15 microns or less.
 6. Thecomposition of claim 1 wherein the settable composition has a density ina range of about 4 pounds per gallon to about 20 pounds per gallon, andwherein the water is present in an amount sufficient to form a pumpableslurry.
 7. The composition of claim 1 wherein the first cementitiouscomponent comprises at least one component selected from the groupconsisting of Portland cement, calcium aluminate, gypsum, a pozzolanicmaterial, kiln dust, and any combination thereof.
 8. The composition ofclaim 1 wherein the first cementitious component and the secondcementitious component have reactive indexes that vary by a factor of atleast about 100:1.